Transmission of M-state quadrature amplitude modulated (QAM) signals via orthogonally polarized carriers results in the conveyance of increased information within a given bandwidth, resulting further in economic advantages. The main obstacle in the way of realizing these advantages is the unavoidable presence of cross polarization interference (CPI) between the dually polarized signals which arise due to factors such as multipath fading, antenna misalignments, and imperfect waveguide feeds.
The theory of linear and decision feedback equalization/cancellation, to mitigate the effects of intersymbol interference (ISI) and noise in the transmission of a single digital signal, is well established in an article entitled "Digital Communication over Fading Radio Channels," Bell System Technical Journal, Volume 62, Number 2, Part 1, pages 429 to 459, February 1983 by Messrs. G. J. Foschini and J. Salz. But a combination of data aided compensation of CPI cancellation and ISI equalization in the presence of noise in the aforesaid manner has not been solved heretofore.